The present invention relates to a coil arrangement for a nuclear fusion apparatus and more particularly to a transition-feeding structure for the coil arrangement for a nuclear fusion apparatus.
A prior art coil arrangement for a nuclear fusion apparatus is constructed as shown in FIGS. 1 and 2. FIG. 3 is a schematic view showing the flow of the coil current of the coil shown in FIG. 1., the solid line showing the current flowing in the upper coil layer and the dot line showing the current flowing in the lower coil layer. FIG. 4 is a schematic view showing current loops of error magnetic fields causing error magnetic fields namely showing only the current remaining after the elimination of ideal circular current among the currents flowing in the coil of FIG. 3.
Referring now to FIGS. 1 and 2, reference numeral 1 designates a coil conductor, numeral 2 a transition conductor between turns, numeral 3 a transition conductor between layers and numeral 4 a feeder line.
A current flows through the coil conductor 1, but when the current flows in the transition conductor between turns 2, transition conductor between layers 3 and the feeder line 4, additional current components other than the current which flows through the coil conductor 1 are generated since they are deviated from the round shape of the coil as shown in FIGS. 3 and 4. The additional current components generate error magnetic fields which are disadvantageous in that they effect the confinement of plasma within the coil. It is clear that the smaller the loop areas of the additional currents are, the smaller the error magnetic fields become. It has been therefore conceived that the transition structure be changed.
FIG. 5 is a schematic view showing the mode of transition of the current flowing through the coil disclosed in Japanese Patent application laid open No. 59-7287 published on Jan. 14, 1984 "A nuclear fusion apparatus", Applicant: Hitachi Seisakusho K. K. In the fig. reference numeral 5 designates arrows indicating the direction of the current flowing through the coil, numeral 6 a transition current between coil layers, numeral 7 a transition current between coils, and numeral 8 a return conductor. As can be seen from Fig. the transition directions are reversed to each other as indicated by the arrows 6, so as to minimize the error magnetic fields in the inner side of the coil in the vicinity of the plasma (not shown).
However, even with the prior art technic as shown in FIG. 5, there exists the possibility of the problem that current loops may remain and generate the error magnetic fields, since the error magnetic fields may not be cancelled out sufficiently. Furthermore, there exists the problem in the production of the coil due to the fact that the mode of transition between coil layers is complicated.